Recently, semiconductor devices such as a LSI, IC, transistor or the like have been encapsulated by transfer molding with an epoxy resin. For instance, surface mounting of LSI devices has been conducted. In the latter regard, a process involving direct immersion in a solder bath is becoming more common. During the immersion, the encapsulating material is exposed to a high temperature not lower than 200.degree. C. However, the encapsulating material contains water. As a consequence, the moisture contained in the encapsulating material is vaporized and expanded which causes cracks or peeling at the interface with a die pad.
Currently the most popular encapsulating materials are based on an epoxy resin which is a glycidyl ether of o-cresol novolak together with a phenol novolak as a curing agent. The encapsulating materials comprising mainly glycidyl ethers of o-cresol novolak and phenol novolaks must achieve some balance between the competing properties of heat resistance and moldability. However, these popular materials are not sufficient for use in applications which require a high level of non-hygroscopicity as described above, and suffer the added drawback of solder cracking. As a practical matter, these encapsulating materials are marketed in the wrapped form with moisture-proof wraps to avoid the above-noted problems with hygroscopicity.
In view of the above and other drawbacks, the art has sought to provide encapsulating resin materials which are even less hygroscopic, exhibit improved resistance to cracking and show higher adhesiveness.